The Halloween Release

  * Improved translations:
    - French: mission and engine back at 100%
    - Brazilian: missions at 58%
  * Engine:
    - #292: Check the user's input before submitting a feedback
    - #304: Stop user's program's or demo's execution if the user
      switches to another exercise or lesson.
    - #395: Correctly remove the files that should be when reverting
      or failing an exercise (both in local and remote repositories)
    - #389: Allow fullscreen on Mac OSX
    - #394: Display a waiting dialog when exiting
    - #263: Also interpret language tags in hints, not only missions
    - #401: Remove non-needed HumanLangListeners
    - Greatly improve the coverage of our unit tests.
  * Worlds:
    - #286: Turtle, Buggle: document where (0,0) is
    - #220: Buggle: Improve doc of isOverBaggle(), isCarryingBaggle()
  * Pedagogical content:
    - #323: turtleart.Kerr40: new exercise
    - #397: GnomeSort: align mission text with code
    - #296: TraversalByColumn: document where (0,0) is
    - #239: CourseForest: get stick in water, not moving anymore
    - #405: LoopStairs: Make French python bindings fit the templating
    - #406: Lander101: unclear mission text wrt stepping the simulation
    - #409: LoopWhile: additional reference to "About this world" menu